The Collaborative International Dictionary of English v.0.48:

Jeer \Jeer\, v. i. [imp. & p. p. Jeered; p. pr. & vb. n.
   Jeering.] [Perh. a corrup. of cheer to salute with cheers,
   taken in an ironical sense; or more prob. fr. D. gekscheren
   to jeer, lit., to shear the fool; gek a fool (see 1st Geck)
   + scheren to shear. See Shear, v.]
   To utter sarcastic or scoffing reflections; to speak with
   mockery or derision; to use taunting language; to scoff; as,
   to jeer at a speaker.
   [1913 Webster]

         But when he saw her toy and gibe and jeer. --Spenser.

   Syn: To sneer; scoff; flout; gibe; mock.
        [1913 Webster]

The Collaborative International Dictionary of English v.0.48:

Jeering \Jeer"ing\, a.
   Mocking; scoffing. -- n. A mocking utterance. --
   Jeer"ing*ly, adv.
   [1913 Webster]

WordNet (r) 3.0 (2006):

jeering
    adj 1: abusing vocally; expressing contempt or ridicule;
           "derisive laughter"; "a jeering crowd"; "her mocking
           smile"; "taunting shouts of `coward' and `sissy'" [syn:
           derisive, gibelike, jeering, mocking, taunting]
    n 1: showing your contempt by derision [syn: jeer, jeering,
         mockery, scoff, scoffing]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "jeering":
   affront, aspersion, atrocity, banter, bantering, booing, brickbat,
   catcalling, chaffing, contempt, contumely, cut, derision, derisive,
   derisory, despite, dump, enormity, fleering, flippancy, flippant,
   flout, flouting, fooling, gibe, grinning, hissing, hooting,
   humiliation, indignity, injury, insult, jeer, joshing, kidding,
   leering, levity, mock, mockery, mocking, offense, outrage, panning,
   put-down, quizzical, ragging, railing, raillery, rallying, razzing,
   ridicule, ridiculing, roasting, scoff, scoffing, scurrility, smart,
   smart-aleckiness, smart-alecky, smart-ass, smartness, smirking,
   sneering, snickering, sniggering, snorting, taunt, taunting,
   teasing, twitting, uncomplimentary remark